The present invention relates to a variable magnification copying apparatus in which the focal distance of the optical system thereof is made variable stepwise and thereby either of the copied images can be reduced or magnified in size.
As for the copying apparatus of this kind, there have been known one as shown in FIG. 1 which is a schematic illustration of the optical system of an optical system reciprocation type copying apparatus.
In FIG. 1, an original pattern placed on a glass plate 2 is projected onto a photosensitive receptor drum 8 by means of light from an exposure lamp 1 through a first mirror 3, a second mirror 4, a third mirror 5, a projection lens 6 (mounted to a light shielding base board 12) and a fourth mirror 7, while keeping the distance from the original pattern to the projection lens 6 unchanged by sliding the mirrors 4 and 5 along a guide-roller 9 at half the speed of the constant speed at which the exposure lamp 1 is slid. The original pattern is formed into an electrostatic latent image on the photosensitive receptor drum 8 which rotates synchronously. For attaining a copy reduction or magnification, the projection lens 6 on a carrier is moved to a certain distance in the direction of the optical axis thereof and compensation lenses 10 are automatically interposed in the optical path of the projection lens 6 so as to compensate the aspect ratio of the image pattern in accordance with the correlation between the optical system and the photosensitive receptor drum 8 being rotated at a constant speed.
In such a conventional variable magnification type copying apparatus, the movements of the projection lens 6 and the interposition of the compensation lenses 10 have been performed by controlling the operation (movement and stop in motion) of a motor through such a controller as a microcomputer provided in the main body of a copying apparatus with a driving mechanism comprising an A.C. motor and chain-sprockets, a microswitch for detecting the position of the projection lens, an electromagnetic clutch for connecting to the carrier for the projection lens, a brake for stopping the movement and the like.
The conventional type apparatus of this kind has generally used A.C. motors and therefore the power unit thereof has unnecessarily increased in size, and the lens movement unit thereof has also required a guide-member which is expensive and large-sized, such as a combination unit of a shaft member and a slide member, or a built-in steel rail, in order to guide a relatively heavy load with a high accuracy. The abovementioned facts have partly necessitated the whole body of a copying apparatus to be made relatively large in size. In the conventional apparatus, it has also been difficult to combine a unit for moving the projection lens and the driving unit thereof into a single body to save space in the apparatus. Therefore many disadvantages have still remained unsolved in the assembly work, adjustments and maintenance services because it has taken time and trouble to combine and position these two units when the optical system is mounted to the body of apparatus.